Whether or not to flatten the top of the tool (aka rake angle) is a matter of preference, and is entirely situational, just as "pushing vs dragging" when doing conventional turning. I almost always "drag" the bit when turning, and also use a negative (tipped down into the thread) rake angle for threading as I find it a bit easier on the tool. Contrary to what some on here have or will say, its entirely personal opinion, and many professionals do it both ways. To support this to the naysayers, many carbide manufacturers recommend negative rake and dragging, and many carbide holders are manufactured this way.
As to your other question about the angle of the tool bit relative to the ways, it should always be perpendicular to the ways when threading, not at an angle as shown in your second 3d model.
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